Miniaturized radio frequency antenna

ABSTRACT

A device and method for receiving signals in the radio frequency range by a mobile phone. The device comprises a radiator part having a ¼ wave electric length (or an odd integral multiple thereof) for receiving the signals, wherein the feed of the radiator part is tapped for impedance matching. In order to reduce to the size of the device so that it can be implemented in a mobile phone or a communicator, the radiator part is placed at the proximity of a frame having a medium relative permittivity for dielectric loading. The relative permittivity of the frame ranges from 2 to 50 in the radio frequency range. Preferably, one or more devices are placed at one of the corners of the mobile phone body so that one device will be selected to receive the signals based on the interaction between the radiation modes of the device and the radiation field of the mobile phone body in order to achieve a right-handed, circular or elliptical polarization.

FIELD OF THE INVENTION

[0001] The present invention relates generally to an antenna fortransmitting and receiving electromagnetic waves carrying messages inthe radio frequencies and, in particular, to Global Positioning System(GPS) antennas operating in the 1575.42 MHz frequency band.

BACKGROUND OF THE INVENTION

[0002] A CDMA telephony system is based on spread-spectrum technologyand is one of the most widely used digital wireless services today. Thespread-spectrum signal requires sophisticated broadcast power managementand soft hand-overs between base stations. This means that the basestations must be precisely timed. With the CDMA wireless telephonysystem, each transmitter must maintain its frequency to within one partin ten billions. It is advantageous and desirable to have an antenna ina mobile phone so as to allow the mobile phone to receive messages inthe CDMA as well as WCDMA system. Furthermore, the U.S. FederalCommunications Commission has introduced regulations requiring wirelessservice providers to supply the location of all system users foremergency situations. In particular, the Wireless Communications andPublic Safety Act, also known as E-911, makes 911 the universalemergency number for wireless telephones so that the cellular user whohas been in an accident can be automatically located. Thus, it isadvantageous and desirable to provide a positioning antenna in a mobilephone.

[0003] Currently, GPS technology enables accurate timing andsynchronization between base stations so that cellular calls can beflawlessly passed from one base station to another. The GPS satellitestransmit two microwave carrier signals: the L1 frequency (1575.42 MHz)which carries the navigation message and the Standard PositioningServices (SPS) code signals; and the L2 frequency (1227.60 MHz) which isused for ionospheric delay measurement carried out by the PrecisePositioning Services (PPS) equipped receivers. Three binary codes areused to shift the L1 and/or L2 carrier phases: 1) the Coarse Acquisition(C/A) Code, which is a repeating 1.023 MHz Pseudo Random Noise (PRN),code-modulates the L1 carrier phase, spreading the spectrum over a 2.046MHz bandwidth, or a larger bandwidth such as 10 MHz. For the code-phasemodulation, each GPS satellite is assigned a different C/A code PRN, sothat each GPS satellite can be identified by a unique PRN code; 2) thePrecise (P) Code uses a 10.23 MHz PRN code for modulating both the L1and L2 carrier phases for the military receivers; and 3) the navigationmessage, which is used to modulate the L1-C/A or P(Y) code signal, is a50 Hz signal consisting of data bits that describe the GPS satelliteorbits, system time, position, clock corrections, and other systemparameters.

[0004] As described above, GPS provides both the Standard PositioningService (SPS) and the Precise Positioning Service (PPS). Only the SPS isdesignated for the civil community. Thus, in order to receive signalsbroadcast from the GPS satellites, the antenna should be tuned to the L1band with a suitable bandwidth. The GPS antenna is required to beright-handed circularly polarized (RHCP) or right-handed ellipticallypolarized (RHEP) and to provide near hemispherical coverage in order toachieve optimum performance.

[0005] In a mobile phone, a communicator device or other small hand-heldelectronic device, it is preferable for the GPS antenna to be small insize and rugged. Preferably, the antenna can be mass-produced withoutindividual tuning in order to reduce cost. Currently, a number of smallsize antennas are used in small electronic devices. U.S. Pat. No.5,986,609 (Spall) discloses an antenna configured to be enclosed withinthe flip cover of a radiotelephone and to resonate in three frequencybands including a GPS L1 band. The disclosed antenna is a half-wavedipole antenna which includes two tapered radiating elements located onopposite sides of a substrate. Although the disclosed antenna isintended to be used in a radiotelephone, its implementation isrestricted in that the antenna cannot be placed differently to improvethe radiation efficiency. Furthermore, the size of the antenna is notsmall enough to be implemented within the phone body. In an articleentitled “Design of GPS Microstrip Antenna using Nearly Square Patch”(1997 Asia Pacific Microwave Conference), Chih-Yu Huang et al. disclosesa ceramic patch design. Ceramic patches are known to be compact.However, small ceramic patch antennas are extremely narrow-banded andneed to be individually tuned. In the monograph entitled “Antennas”(McGraw-Hill 1988), Kraus discusses a quadrifilar helix in which each ofthe four (½)λ wires forms a half-turn of a helix on a cylindrical frame.However, the quadrifilar helical antennas as disclosed are unpracticallylarge for mobile phones and small-sized, hand-held devices.

SUMMARY OF THE INVENTION

[0006] It is, therefore, an object of the present invention to provide aminiature circularly or elliptically polarized antenna having sufficientgain which can be mounted on or enclosed within a mobile phone or otherminiature hand-held electronic device. In particular, the antenna isdesigned to resonate over the GPS frequency bands or other radiofrequency bands with improved radiation efficiency over the existingminiature antennas.

[0007] It is another object of the present invention to provide a methodof installing miniature antennas in a mobile phone or other hand-heldelectronic device in order to achieve an improved axial ratio.

[0008] According to one aspect of the present invention, the radiofrequency antenna comprises a radiating element implemented on asupporting frame. In order to match the impedance of the radiatingelement, the feed of the radiating element is tapped. Thus, one end ofthe radiating element is short-circuited to a ground plane and the feedpoint of the antenna is located at the close proximity of the groundingpoint. Preferably, the radiating element is substantially equal to aquarter-wave electric length or an odd integral multiple thereof. It isalso preferred that the supporting frame be made of a material having amedium relative permittivity so as to effect dielectric loading to theantenna in order to reduce the size thereof. The relative permittivityof the support frame material can range from 2 to 50 in the radiofrequency range. Preferably, the relative permittivity of the supportingframe material ranges from 2 to 50 in the GPS frequency range. With thisdielectric loading technique, the size of the antenna can besubstantially reduced.

[0009] According to the preferred embodiment of the radiating antenna,the radiating element has a helical shape spiraling around thesupporting frame.

[0010] According to another embodiment of the antenna, the radiatingelement is shaped like a single meander line on a surface of thesupporting frame.

[0011] The method of receiving signals in the radio frequency range by amobile phone, according to another aspect of the present invention,comprises the steps of:

[0012] providing a radiator part having substantially a quarter-waveelectric length to receive electromagnetic waves containing the signals;and

[0013] providing means for effecting dielectric loading on the radiatorpart in order to reduce the size thereof.

[0014] In particular, the radiator part includes a signal conduit partjoining the radiator part at a feed point in order to retrieve thesignals from the radiator part; and an impedance matching part joiningthe radiator part at the proximity of the feed point in order to matchthe impedance of the radiator part.

[0015] A further aspect of the present invention is a method ofachieving a right-handed circularly or elliptically polarized antenna ina mobile phone, wherein the mobile phone has a phone body having fourcorners to define a plane having a long axis and a short axis. Themethod comprises the steps of: providing at one of the phone bodycorners a radiator part having substantially a quarter-wave electriclength to generate a radiating mode along the long axis and anotherradiating mode along the short axis; providing a support frame locatedat the proximity of the radiator part to effect dielectric loading onthe radiator part in order to reduce the size thereof. Furthermore, theradiator part includes a resonating region and a feeding region, whereinthe feeding region has a signal conduit part joining the resonatingregion at a feed point in order to retrieve signals from the resonatingregion; and an impedance matching part joining the resonating region atthe proximity of the feed point.

[0016] It should be noted that the radiator part as described above isdivided into a resonating region and a feeding region only in a loosesense. The feeding region, to some extent, also affects the resonatingproperties of the antenna as it also affects the radiating modes of theantenna.

[0017] Alternatively, two or more antennas can be implemented ondifferent corners of the substrate so that one antenna can be selectedby switching means to achieve improved circular or ellipticalpolarization.

[0018] A further aspect of the present invention is an electronic devicehaving means for receiving signals in the radio frequency range, whereinthe receiving means comprises: a radiator part having substantially aquarter-wave electric length implemented on a support frame having amedium relative permittivity for effecting dielectric loading on theradiator part; and means for matching the impedance of the radiatorpart.

[0019] The present invention will become apparent upon reading thedescription taken in conjunction with FIGS. 1-9 c.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 is an isometric view showing a helical antenna, accordingto the preferred embodiment of the present invention.

[0021]FIG. 2 is an exploding view showing the preferred location forimplementing the radio frequency antenna in a mobile phone.

[0022]FIG. 3 is a perspective view showing a mobile phone having amobile phone antenna and a radio frequency antenna.

[0023]FIGS. 4a-4 c are diagrammatic representations showing differentimplementations of the radio frequency antenna on a Printed-CircuitBoard (PCB).

[0024]FIG. 5 is a diagrammatic representation showing a method of tuningthe PCB for optimizing the polarization purity of the radio frequencyantenna.

[0025]FIG. 6 is a diagrammatic representation showing a method ofachieving an improved circular or elliptical polarization.

[0026]FIG. 7 is an isometric view showing another embodiment of thepresent invention.

[0027]FIG. 8 is a plot showing the bandwidth of a helical antenna incomparison with the bandwidth of a ceramic patch antenna.

[0028]FIGS. 9a-9 c are plots showing the radiation pattern of a mobilephone having a helix antenna in different planes.

DETAILED DESCRIPTION OF THE INVENTION

[0029] As shown in FIG. 1, the radio frequency or GPS antenna 10includes an electrically conducting radiating element 20 constructedaround a supporting block 30. Preferably, the supporting block 30 ismade of a material having a relative permittivity in the range of 2 to50 so as to effect dielectric loading to the antenna. Dielectric loadingis used so that the size of the antenna can be suitably reduced so thatthe antenna can be used in a mobile phone or other small hand helddevices. The approximate dimensions of the supporting block 30 aredenoted by H, W and T. In an exemplary GPS antenna, the support block 30is made of a plastic having a relative permittivity of approximately 10in the GPS frequency range, and the dimensions of the supporting block30 are approximately H=9 mm, W=5 mm and T=3 mm. However, the dimensionscan be larger or smaller. Preferably, the radiating element 20 has ahelical shape spiraling around the supporting block 30. Preferably, thefeed of the radiating element 20 is tapped for impedance matching.Accordingly, one end of the radiating element 20 is short-circuited to aground (not shown) by a grounding pin 22, and a feeding pin 24 isconnected to the radiating element 20 to provide a feed point at theclose proximity of the grounding point. As such, the radiating element20 constitutes the resonating region of the antenna while the groundingpin 22 and the feeding pin 24 constitute the feeding region of theantenna. The feeding pin 24 is used as a signal conduit to retrievesignals from the resonating region while the ground pin 22 is used as animpedance matching part for matching the impedance of the resonatingregion.

[0030] As shown, the radiating element 20 which is a helix having twoand a half turns to make up a length of approximately 50 mm. Partly dueto the shape of the radiating element 20 and partly due to the mediumrelative permittivity of the supporting frame 30, the size of theantenna 10 is sufficiently small to be installed in a mobile phone orother hand-held electronic device. In this exemplary antenna, the widthsA, B, D of the radiating element 20, grounding pin 22 and feeding pin24, respectively, are approximately equal to 1 mm, while the distancebetween the grounding pin 22 and the feeding pin 24 is approximately 3to 5 mm. It is understood that the dimensions of the various parts ofthe antenna 30 can be changed according to the shape of the radiatingelement 20 and the relative permittivity of the supporting block 30.

[0031] As shown in FIG. 2, reference numeral 100 denotes a mobile phoneor a communicator having a front portion 102 including a mobile phoneantenna 103, a chassis 104, a printed-circuit board (PCB) 106 and a backcover 110. It is preferred that the GPS antenna 10, according to thepresent invention, be mounted on the PCB 106.

[0032] When used in an electronic device, such as a mobile phone, whichhas by itself a certain radiating mode, the radio frequency antenna mustbe oriented and placed in such a way that the radiating mode in theantenna is orthogonal and in 90 degree phase shift compared to theradiating mode of the device body. With its reduced size, the radiofrequency antenna according to the present invention has the advantageof being able to be implemented differently and at different parts of anelectronic device. In particular, it is preferred that the radiofrequency antenna be implemented on a corner of the device body with asticking upward position, as shown in FIG. 3.

[0033]FIGS. 4a-4 c are diagrammatic representations showing differentimplementations of the GPS or radio frequency antenna 10 on the PCB 106.Preferably, the GPS antenna 10 is mounted in one of the corners of thePCB 106. When the antenna 10 is placed in a corner of the PCB 106, tworadiating modes are generated in the phone body: one along the Y axisand one along the X axis. Because the wave number of one mode isdifferent from the wave number of the other mode, a phase shift existsbetween the radiation patterns of the two radiation modes. This phaseshift is essential in generating the circular polarization. When theantenna 10 is placed in the upper right corner of the PCB 106 as shownin FIG. 4c or the lower left corner as shown in FIG. 4b, the radiationin the Z direction is right-handed circularly or elliptically polarizedwhile the radiation in the −Z direction is left-handed circularly orelliptically polarized. When the antenna 10 is placed in the upper leftcorner of the PCB 106 as shown in FIG. 4b, the radiation in the Zdirection is left-handed circularly or elliptically polarized while theradiation in the −Z direction is right-handed circularly ellipticallypolarized.

[0034] It is possible to tune the radiating mode of the phone body bycutting one or more slits 107 on the PCB 106 as shown in FIG. 5. Byadjusting the size of the slit 107, the polarization purity of the GPSantenna 10 placed on a phone body can be optimized.

[0035] It is also possible that two or more antennas 10, preferablyidentical, are placed in different corners of the PCB 106 so that oneantenna 10 is selected to achieve optimum performance. Because theradiation of the device body where the antenna is implemented may varydepending on the design of the device, the one antenna that yields thebest response can be selected for receiving the GPS signals by anelectronically controlled device such as a pin diode, a MicroElectro-Mechanical Switch (MEMS). FIG. 6 shows two GPS antennas 10 areplaced in the upper corners of the PCB 106.

[0036]FIG. 7 shows another embodiment of the radiating element of theGPS or radio frequency antenna. As shown, the radiating element 40 ofthe GPS antenna 12 is a meander line having a grounding pin 42 and afeeding pin 44. The meander line can be implemented on one or moresurfaces of the supporting block 30.

[0037] The miniature antenna of the present invention has a broaderbandwidth than a compact ceramic patch antenna operating at the GPSfrequencies. As shown in FIG. 8, the dash line represents the responseof a helical GPS antenna according to the present invention, while thesolid line represents the response of a typical ceramic patch antenna.The helix GPS antenna has a bandwidth of approximately 80 MHz, as shownat the −6dB points on the plot.

[0038]FIGS. 9a-9 c are plots showing the right-handed circular orelliptical polarization radiation patterns of the helix antenna indifferent planes of the phone body. When the GPS antenna 10 isimplemented on the PCB 106 as shown in FIG. 4a or FIG. 4b, the radiatingpattern of a mobile phone having a helical GPS antenna at the GPSfrequencies in a plane parallel to the WT plane of the antenna is shownin FIG. 9a. Similarly, the radiating pattern in a plane parallel to theHT plane of the antenna is shown in FIG. 9b while the radiation patternin the HW plane is shown in FIG. 9c.

[0039] Thus, the present invention has been disclosed according to thepreferred embodiment of a normal mode monofilar helical antenna withdielectric loading and tapped feed. It will be understood that the shapeof the radiating element and the shape of the supporting block can bechanged without departing from the spirit and the scope of the presentinvention. For example, the radiating element can be shaped as a meanderline as shown in FIG. 7 or a combination of a meander line and a helix.The λ/4 wire (the radiating element) can also be twisted in manydifferent ways. Furthermore, the radiating element can be a (¾)λ or a({fraction (5/4)})λ, and so forth. It should be noted that the majorradiation in a mobile phone (or other hand-held device) is coming fromthe phone body. Depending on the location of the GPS antenna on thephone body, different radiating modes are generated to the phone body.Thus, the radiation properties of the antenna and the phone dependconsiderably on the location of the GPS antenna.

[0040] Furthermore, although the present invention has been describedmostly in terms of the GPS frequency range, it will be understood thatthe antenna, according to the present invention, is applicable to allradio frequencies and it can also be used in a wireless device, such asa mobile phone, to receive messages or signals in the CDMA and WCDMAsystems.

[0041] Thus, it will be understood that the foregoing is illustrative ofthe present invention and is not to be construed as limited to thespecific embodiments disclosed. The scope of the invention is defined bythe following claims, with equivalents of the claims to be includedtherein.

What is claimed is:
 1. An antenna operating in the radio frequency rangecomprising: a radiator part; and a support frame for effectingdielectric loading on the radiator part, wherein the radiator partcomprises a resonating region for receiving signals and a feeding regioncoupled to the resonating region for impedance matching.
 2. The antennaof claim 1, wherein the support frame has a relative permittivityranging from 2 to 50 in the radio frequency range.
 3. The antenna ofclaim 1, wherein the support frame has a relative permittivity rangingfrom 2 to 50 in a GPS frequency section of the radio frequency range. 4.The antenna of claim 1, wherein the resonating region has a helicalshape spiraling around the support frame.
 5. The antenna of claim 1,wherein the resonating region has a meander line pattern disposed on asurface of the support frame.
 6. The antenna of claim 1, wherein thesupport frame is quadrilateral.
 7. The antenna of claim 1, wherein theresonating region is produced by metal plating directly on the supportframe.
 8. A method of receiving signals in the radio frequency range bya wireless hand-held device, said method comprising the steps of:providing means for receiving electromagnetic waves containing thesignals; and providing means for effecting dielectric loading on theradiator part in order to reduce the size thereof.
 9. The method ofclaim 8, wherein the receiving means comprises: a resonating regionhaving an impedance; and a feeding region including a signal conduitpart joining the resonating region at a feed point in order to retrievethe signals from the resonating region, and an impedance matching partjoining the resonating region at the proximity of the feed point inorder to match the impedance of the resonating region.
 10. The method ofclaim 8, wherein the dielectric loading is achieved by using a supportframe having a medium relative permittivity located at the proximity ofthe receiving means.
 11. The method of claim 10, wherein the relativepermittivity ranges from 2 to 50 in the radio frequency range.
 12. Themethod of claim 10, wherein the relative permittivity ranges from 2 to50 in a GPS frequency section of the radio frequency range.
 13. Themethod of claim 10, wherein the resonating region has a helical shapespiraling around the support frame.
 14. The method of claim 10, whereinthe resonating region has a meander line pattern disposed on a surfaceof the support frame.
 15. The method of claim 8, wherein the hand-helddevice has a radiation field and the receiving means is placed at alocation in the hand-held device in order to achieve a right-handedcircular or elliptical polarization according to the radiation field ofthe hand-held device.
 16. The method of claim 8, wherein the hand-helddevice is a mobile phone.
 17. The method of claim 8, wherein thehand-held device is a communicator.
 18. An antenna operating in theradio frequency range to be used in a wireless device comprising: aradiator part; and a support frame having a relative permittivity in therange of 2 to 50 in the radio frequency range for effective loading onthe radiator part in order to reduce the size thereof, wherein theradiator part comprises a resonating region having a helical shapeimplement on the support frame, and a feeding region comprising meansfor retrieving signals received by the resonating region and means forimpedance matching.
 19. The antenna of claim 18, wherein the supportframe is made of plastic.
 20. The antenna of claim 18, wherein theradiator part is implemented on the support frame by metal plating. 21.The antenna of claim 18, wherein the wireless device is a mobile phone.22. The antenna of claim 18, wherein the wireless device is acommunicator.
 23. A telephone device having communication meansoperating in the radio frequency range, wherein said communication meanscomprises: means for receiving electromagnetic waves containingcommunication signals, and means for effecting dielectric loading on thereceiving means in order to reduce the size thereof.
 24. The device ofclaim 23, wherein the receiving means has an impedance, the devicefurther comprising: means coupled to the receiving means for matchingthe impedance thereof.
 25. A method of achieving a right-handedcircularly or elliptically polarized antenna in a wireless device havinga device body for mounting the antenna, wherein the phone body has fourcorners to define a plane having a first axis and a second axis, saidmethod comprising the steps of: providing at one of the corners of thedevice body a radiator part to generate a first radiating mode along thefirst axis and a second radiating mode along the second axis such that aphase shift exists between the first radiating mode and the secondradiating mode; and providing means for effecting dielectric loading onthe radiator part.
 26. The method of claim 25, wherein the first andsecond radiating modes form an antenna radiating mode and the devicebody has a third radiating mode, wherein the antenna radiating mode isorthogonal to the third radiating mode.
 27. The method of claim 26,wherein the antenna radiating mode has a substantially 90 degree phaseshift compared to the third radiating mode.
 28. The method of claim 25,wherein the antenna is operating in a radio frequency range and whereinthe dielectric loading means has a relative permittivity ranging from 2to 50 in the radio frequency range and is located at the proximity ofthe radiator part in order to effect dielectric loading.
 29. The methodof claim 25, wherein the antenna is operating in a GPS frequency rangeand wherein the dielectric loading means has a relative permittivityranging from 2 to 50 in the GPS frequency range and is located at theproximity of the radiator part in order to effect dielectric loading.30. A method of achieving a right-handed circularly or ellipticallypolarized radiation field for receiving signals in the radio frequencyrange by a wireless device having a device body generating a bodyradiation field, said method comprising the steps of: providing aplurality of radio frequency antennas on the device body, wherein eachradio frequency antenna has a radiation pattern; and selecting one ofthe radio frequency antennas according to the interaction between theradiation pattern of each radio frequency antenna and the body radiationfield of the device body in order to achieve an optimum performance ofthe circularly or elliptically polarized radiation field.
 31. The methodof claim 30, wherein each of the radio frequency antennas comprises: aradiator part; and a support frame located at the proximity of theradiator part for effecting dielectric loading on the radiator part. 32.The method of claim 31, wherein the support frame has a relativepermittivity ranging from 2 to 50 in the radio frequency range.
 33. Themethod of claim 31, wherein the support frame has a relativepermittivity ranging from 2 to 50 in a GPS frequency section of theradio frequency range.
 34. The method of claim 30, wherein the selectionof the radio frequency antennas is achieved by using a pin diode. 35.The method of claim 30, wherein the selection of the radio antennas isachieved by using a micro electro-mechanical switch.